This invention relates to assembly tools for installing piston and connecting rod assemblies in an engine.
A common method of installing a piston/connecting rod assembly in an engine cylinder involves sliding a piston ring compressor sleeve (ring compressor) over the skirt and piston rings of the piston and manually inserting the connecting rod end of the assembly into the outer end of the engine cylinder. The piston/rod assembly is slid into the cylinder until the ring compressor engages the outer end of the engine cylinder. A guide finger may be utilized on the crank end of the connecting rod to guide the connecting rod in the cylinder and align the bearing recess with the crankpin of the engine crankshaft. The assembly is then forced into the engine cylinder so that the piston rings compressed by the ring compressor are guided into the cylinder and the piston is forced inward until the connecting rod bearing recess or bearing insert engages the engine crankpin. This xe2x80x9cstuffingxe2x80x9d step may be accomplished manually, such as by applying force against a stuffing block engaging the piston head. Automatic piston installing machinery has also been developed but it is very expensive to make as well as to maintain.
A form of manually-operated tool which is in common use in many engine assembly plants utilizes a manually-operated lever arm that is pivotable by the operator and has a roller that is moved into engagement with the piston head. The lever arm has a handle which is grasped by the operator and provides a mechanical advantage to assist the operator in pivoting the arm to force the piston through the ring compressor and into the cylinder until the connecting rod engages the associated crankpin. As the piston is forced into the cylinder, the ring compressor slides off and is caught by a hook on the lever arm as the arm is retracted by the operator. A biasing spring assists the retraction and holds the arm out of the way for insertion of the next piston/rod assembly.
Over a number of years, piston compression ring tension has been increasing in order to reduce the amount of piston ring blowby to better control exhaust emissions. The increased ring tension has tended to increase the force the operator must apply to overcome the ring tension acting against the cylinder as the piston is inserted into the cylinder bore. In order to reduce the effort required for this process, an assembly tool has been desired which could significantly reduce operator effort while being capable of construction at a reasonable cost and application to current and future assembly lines without requiring the significant outlays of capital required for a fully automatic machine.
The present invention provides a semi-automatic engine piston assembly tool which can be applied in place of the manual tool currently used in many assembly lines. The new tool utilizes a pivoting support arm which is controlled and moved into position by the operator grasping a handle in a manner similar to the prior manually actuated tool. However, the tool is provided with an air insertion cylinder, mounted on the end of the arm, that is moved into a position so that the piston head is engaged by the end of an insertion rod actuatable by the cylinder. A ring compressor retractor is carried on the end of the insertion rod.
The pivoting support arm is biased upwardly into a loading position by a balancing cylinder which utilizes low pressure air to retract the arm to the loading position. A piston/rod assembly is then loaded through the outer end of the engine cylinder with a ring compressor on the piston and engaging the engine cylinder outer end.
The operator manually moves the support arm into the insertion position with the end of the insertion rod against the piston head. The operator actuates and holds a trigger switch, which applies high pressure to lock the support arm in position and applies controlled air pressure to the insertion cylinder. This causes the insertion rod to advance through the ring compressor and force the piston/rod assembly into the engine cylinder until a bearing recess or bearing insert of the connecting rod engages the associated crankpin.
At this point, the ring compressor slides downward and is captured on the face of the ring retractor. A magnet on the retractor retains the steel ring compressor on the angled face of the retractor and allows the flange of the ring compressor to fall into a hook-like groove at the bottom of the retractor member. The operator then releases the trigger switch, which retracts the insertion rod into the insertion cylinder carrying the ring compressor with it. The support arm is then allowed to be raised by the balancing cylinder, carrying with it the ring compressor mounted to the face of the ring retractor at the end of the insertion rod. The tool is then moved on a carriage longitudinally along the side of the engine to the next cylinder position and a piston/rod assembly with the ring compressor attached is installed into the next cylinder for repetition of the assembly operation.
The semi-automatic assembly tool significantly reduces operator required effort since the force required for stuffing the piston into the cylinder is applied by the insertion air cylinder. At the same time, the improved operation with the automatic insertion and retraction steps is accomplished with a relatively simple but effective mechanism which can be applied to current assembly lines with a minimum of disturbance to the established features of the line. In addition, the tool is applicable to new assembly lines which can be fitted and installed at a relatively reasonable cost as compared to automatic machines which are both expensive and costly to maintain.